The invention relates to a stud welding device with an adjustment member, displaceable axially forward and backwards, a stud holder, connected to the adjustment member, so the movement thereof is transmitted to the stud holder, a drive unit, having a coil which can be connected to a source of current, the coil being rigidly attached to a hollow body connected to the adjustment member, because it is arranged as axially movable in an air gap between a magnetisable core and a magnetisable casing, and with a compression spring acting on the adjustment member, pressing this into an end position defined by a buffer.
A stud welding device of this kind is known from the German Patent Publication No. 44 37 264. In this stud welding device the axial forces acting on the coil and thus on the hollow body with the adjustment member can be accurately dimensioned to any position within the adjustment path of the coil. Accuracy in setting the adjustment member is also achieved in the known stud welding device in that a spring acts on the adjustment member, pressing it into an end position defined by a buffer. If the spring force generated by the spring force [sic] acts against the axial force produced by the coil, the axial force has to overcome this spring force, which means that the adjustment member is lifted from its buffer. The axial force needed for this can be accurately set by setting a corresponding current flowing via the coil, so the course of the spring force can also be allowed for.
Based on this, the object of the invention is to further develop the known stud welding device in such a way that the constructive assembly of the stud welding device is simplified.
The stud welding device according to the invention with an adjustment member, displaceable axially forward and backwards, a stud holder, connected to the adjustment member, so the movement thereof is transmitted to the stud holder, a drive unit, having a coil which can be connected to a source of current, the coil being rigidly attached to a hollow body connected to the adjustment member, the hollow body being arranged as axially movable in an air gap between a magnetisable core and a magnetisable casing, and with a compression spring acting on the adjustment member, pressing this into an end position defined by a buffer, is characterised in that the core has a recess extending from a front face adjacent to the adjustment member over at least a part of the axial length of the core, into which the compression spring partially protrudes.
With this configuration of the stud welding device the at least one compression spring forms a part of the drive unit, so the constructive outlay for developing the stud welding device according to the invention is reduced in comparison with known stud welding devices. In particular, because the compression spring is partially arranged in the-core, it is achieved that the structural size of the stud welding device is reduced compared with conventional stud welding devices.
To make it possible for no or only very slight moments to be introduced into the adjustment member, it is proposed that the recess is designed substantially coaxially to the adjustment member. The compression spring, in particular a helical spring, which is supported with its one front face on a floor of the recess and with the opposed front face on the adjustment member, is placed in this recess.
With relatively large adjustment paths of the adjustment member it is necessary for the compression spring to project from the core by at least the same amount as the size of the adjustment path and to press against the front face of the adjustment member. There is a possibility here that, on movement of the adjustment member, the compression spring may become straightened, which would at least impair the operability of the stud welding device. To avoid this, it is proposed, according to a further advantageous development of the invention, that the adjustment member has at least one extension, each extension being encircled in each case by a compression spring. Security against buckling of the compression spring, if this is a helical spring, is increased by the extension.
The forward and backward movement of the adjustment member causes strain and stretching of the compression spring. It can happen, owing to material fatigue of the compression spring, for example, that the compression spring no longer produces a sufficient spring force. It is therefore necessary to replace the compression spring. To be able to carry out the changing of a compression spring of this kind as easily as possible, it is proposed that the at least one recess fully penetrates the core and a seal is provided which closes an orifice of the recess and forms an abutment for the compression spring. In particular it is proposed that the seal is connected detachably to the core. Alternatively the seal can also be connected to a housing cover or similar. It can also form the seal itself.
According to yet another advantageous configuration of the invention it is proposed that the recess has a lining and the compression spring is arranged in this. Preferably the lining and/or the compression spring is made of a magnetically non-conducting or magnetically low-conducting material. In particular the lining consists of a hard plastic material. By these measures it is achieved in an advantageous way that the magnetic field interspersing the coil is not influenced, or only to a very minor extent.
Further details and advantages of the invention are explained using the embodiments shown in the drawings.